For the Cake: preheat oven to 375°F. Spray two 9" round cake pans with baking spray.

Whisk together egg yolks and sugar in large bowl (or bowl of a stand mixer) over low, then medium speed, until creamy and light yellow in color.

Dissolve coffee granules and cocoa powder in hot water and vanilla in a small bowl, getting rid of lumps while stirring. Pour into the egg-sugar mixture, along with canola oil, and beat until well combined.

Sift cake flour and baking powder over mixture a few at a time and mixing each time. Mix until well blended, scraping the sides of the bowl.

Beat egg whites and cream of tartar into stiff peaks in a medium bowl, and fold into the mocha batter, a dollop or two first to liquefy the thick batter, and then in thirds.

Divide the batter between the two cake pans. Bake for 20 to 25 minutes. The cakes are done when the tops become golden brown and the cake tester comes out clean when inserted in the middle.

Let cool for 10 minutes, then carefully remove from pans, set aside right side up. Cool completely before trimming and icing.

For the Buttercream: Whisk sugar and egg whites for 3 to 5 minutes in a small or medium heatproof bowl set over a saucepan of simmering water (water should not touch the bottom of the bowl), until meringue is hot to the touch. The sugar granuls will be dissolved and you will be left with a fluffy marshmallow cream-like froth.

Remove bowl from heat and beat for 5 minutes with a hand mixer set to medium speed. Mixture will be white and creamy in texture.

Add half of the butter and beat with a hand mixer until smooth before adding the next half to combine. Scrape the sides of the bowl with a spatula and give it a quick stir. Beat again on medium-high for another 6 to 10 minutes.

Dissolve cocoa and coffee granules in hot water, and vanilla extract and amaretto in a small bowl. Pour intothe buttercream mixture and beat for 2 minutes, scraping the sides at least once.

To Assemble the Cake: Using an icing bag, pipe